For the improved production of vaccines and therapeutic proteins, a detailed understanding of the metabolic dynamics during batch or fed-batch production is requested. To study the new human cell ...line AGE1.HN, a flexible metabolic flux analysis method was developed that is considering dynamic changes in growth and metabolism during cultivation. This method comprises analysis of formation of cellular components as well as conversion of major substrates and products, spline fitting of dynamic data and flux estimation using metabolite balancing. During batch cultivation of AGE1.HN three distinct phases were observed, an initial one with consumption of pyruvate and high glycolytic activity, a second characterized by a highly efficient metabolism with very little energy spilling waste production and a third with glutamine limitation and decreasing viability. Main events triggering changes in cellular metabolism were depletion of pyruvate and glutamine. Potential targets for the improvement identified from the analysis are (i) reduction of overflow metabolism in the beginning of cultivation, e.g. accomplished by reduction of pyruvate content in the medium and (ii) prolongation of phase 2 with its highly efficient energy metabolism applying e.g. specific feeding strategies. The method presented allows fast and reliable metabolic flux analysis during the development of producer cells and production processes from microtiter plate to large scale reactors with moderate analytical and computational effort. It seems well suited to guide media optimization and genetic engineering of producing cell lines.
A series of Ru-protein-Co biohybrids have been prepared using the electron transfer proteins ferredoxin (Fd) and flavodoxin (Fld) as scaffolds for photocatalytic hydrogen production. The ...light-generated charge separation within these hybrids has been monitored by transient optical and electron paramagnetic resonance spectroscopies. Two distinct electron transfer pathways are observed. The Ru-Fd-Co biohybrid produces up to 650 turnovers of H
utilizing an oxidative quenching mechanism for Ru(ii)* and a sequential electron transfer pathway
the native 2Fe-2S cluster to generate a Ru(iii)-Fd-Co(i) charge separated state that lasts for ∼6 ms. In contrast, a direct electron transfer pathway occurs for the Ru-ApoFld-Co biohybrid, which lacks an internal electron relay, generating Ru(i)-ApoFld-Co(i) charge separated state that persists for ∼800 μs and produces 85 turnovers of H
by a reductive quenching mechanism for Ru(ii)*. This work demonstrates the utility of protein architectures for linking donor and catalytic function
direct or sequential electron transfer pathways to enable stabilized charge separation which facilitates photocatalysis for solar fuel production.
The effect of Zr modification on the catalytic activity of Co/SiO2 was investigated for nonoxidative propane dehydrogenation. Isolated Zr on SiO2 surface sites were prepared by organometallic ...synthesis using Zr(O t Bu)4 as a precursor. The resulting Zr/SiO2 support was functionalized with Co2+ ions via strong electrostatic adsorption. Spectroscopic (diffuse reflectance infrared Fourier transform spectroscopy, UV–vis, electron paramagnetic resonance) and microscopic characterization (transmission electron microscopy, scanning transition electron microscopy) results are consistent with single-site cobalt that preferentially associates with the mono-dispersed Zr at a variety of loadings and Co/Zr ratios. The oxidation state of Co in the as-prepared Co/SiO2 and Co–Zr/SiO2 was both +2 with tetrahedral and octahedral geometries, respectively. In situ X-ray absorption near edge structure and extended X-ray absorption fine structure results confirmed that the oxidation state of Co remained as +2 under reaction condition for both Co/SiO2 and Co–Zr/SiO2 samples and both catalysts have tetrahedral Co2+ as the active catalyst. Despite similar Co coordination environments, the catalytic activity and selectivity was significantly improved by the Zr modification of the silica support versus Co/SiO2. This was attributed to the change in oxygen donor ability and Co–O bond strength of the SiO–Zr–O sites of Co–Zr/SiO2 compared with the SiO– ligands in Co/SiO2. These results show that tuning of the support SiO2 oxygen donation ability by use of an anchoring site (e.g., SiO–Zr–O–) can be used to alter both rate and selectivity of propane dehydrogenation with single-site heterogeneous catalysts. These results also show some preference for Co2+ active sites to associate with SiO–Zr–O– sites over SiO–.
Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while ...electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.
Rare-earth ion dopants in solid-state hosts are ideal candidates for quantum communication technologies, such as quantum memories, due to the intrinsic spin–photon interface of the rare-earth ion ...combined with the integration methods available in the solid state. Erbium-doped cerium oxide (Er:CeO2) is a particularly promising host material platform for such a quantum memory, as it combines the telecom-wavelength (∼1.5μm) 4f–4f transition of erbium, a predicted long electron spin coherence time when embedded in CeO2, and a small lattice mismatch with silicon. In this work, we report on the epitaxial growth of Er:CeO2 thin films on silicon using molecular beam epitaxy, with controlled erbium concentration between 2 and 130 parts per million (ppm). We carry out a detailed microstructural study to verify the CeO2 host structure and characterize the spin and optical properties of the embedded Er3+ ions as a function of doping density. In as-grown Er:CeO2 in the 2–3 ppm regime, we identify an EPR linewidth of 245(1) MHz, an optical inhomogeneous linewidth of 9.5(2) GHz, an optical excited state lifetime of 3.5(1) ms, and a spectral diffusion-limited homogeneous linewidth as narrow as 4.8(3) MHz. We test the annealing of Er:CeO2 films up to 900 °C, which yields narrowing of the inhomogeneous linewidth by 20% and extension of the excited state lifetime by 40%.
Four new molecular Co(II)tetrapyridyl complexes were synthesized and evaluated for their activity as catalysts for proton reduction in aqueous environments. The pyridine groups around the macrocycle ...were substituted for either one or two pyrazine groups. Single crystal X-ray analysis shows that the pyrazine groups have minimal impact on the Co(II)–N bond lengths and molecular geometry in general. X-band EPR spectroscopy confirms the Co(II) oxidation state and the electronic environment of the Co(II) center are only very slightly perturbed by the substitution of pyrazine groups around the macrocycle. The substitution of pyrazine groups has a substantial impact on the observed metal- and ligand-centered reduction potentials as well as the overall H2 catalytic activity in a multimolecular system using the Ru(2,2′-bipyridine)3Cl2 photosensitizer and ascorbic acid as a sacrificial electron donor. The results reveal interesting trends between the H2 catalytic activity for each catalyst and the driving force for electron transfer between either the reduced photosensitizer to catalyst step or the catalyst to proton reduction step. The work presented here showcases how even the difference of a single atom in a molecular catalyst can have an important impact on activity and suggests a pathway to optimize the photocatalytic activity and stability of molecular systems.
K‐theory Soergel bimodules Eberhardt, Jens Niklas
The Bulletin of the London Mathematical Society,
March 2024, 2024-03-00, Volume:
56, Issue:
3
Journal Article
Peer reviewed
Open access
We initiate the study of K$K$‐theory Soergel bimodules, a global and K$K$‐theoretic version of Soergel bimodules. We show that morphisms of K$K$‐theory Soergel bimodules can be described ...geometrically in terms of equivariant K$K$‐theoretic correspondences between Bott–Samelson varieties. We thereby obtain a natural categorification of K$K$‐theory Soergel bimodules in terms of equivariant coherent sheaves. We introduce a formalism of stratified equivariant K$K$‐motives on varieties with an affine stratification, which is a K$K$‐theoretic analog of the equivariant derived category of Bernstein–Lunts. We show that Bruhat‐stratified torus‐equivariant K$K$‐motives on flag varieties can be described in terms of chain complexes of K$K$‐theory Soergel bimodules. Moreover, we propose conjectures regarding an equivariant/monodromic Koszul duality for flag varieties and the quantum K$K$‐theoretic Satake.
The energy transfer and charge separation kinetics in core Photosystem I (PSI) particles of
Chlamydomonas reinhardtii has been studied using ultrafast transient absorption in the ...femtosecond-to-nanosecond time range. Although the energy transfer processes in the antenna are found to be generally in good agreement with previous interpretations, we present evidence that the interpretation of the energy trapping and electron transfer processes in terms of both kinetics and mechanisms has to be revised substantially as compared to current interpretations in the literature. We resolved for the first time i), the transient difference spectrum for the excited reaction center state, and ii), the formation and decay of the primary radical pair and its intermediate spectrum directly from measurements on open PSI reaction centers. It is shown that the dominant energy trapping lifetime due to charge separation is only 6–9
ps, i.e., by a factor of 3 shorter than assumed so far. The spectrum of the first radical pair shows the expected strong bleaching band at 680
nm which decays again in the next electron transfer step. We show furthermore that the early electron transfer processes up to ∼100
ps are more complex than assumed so far. Several possibilities are discussed for the intermediate redox states and their sequence which involve oxidation of P700 in the first electron transfer step, as assumed so far, or only in the second electron transfer step, which would represent a fundamental change from the presently assumed mechanism. To explain the data we favor the inclusion of an additional redox state in the electron transfer scheme. Thus we distinguish three different redox intermediates on the timescale up to 100
ps. At this level no final conclusion as to the exact mechanism and the nature of the intermediates can be drawn, however. From comparison of our data with fluorescence kinetics in the literature we also propose a reversible first charge separation step which has been excluded so far for open PSI reaction centers. For the first time an ultrafast 150-fs equilibration process, occurring among exciton states in the reaction center proper, upon direct excitation of the reaction center at 700
nm, has been resolved. Taken together the data call for a fundamental revision of the present understanding of the energy trapping and early electron transfer kinetics in the PSI reaction center. Due to the fact that it shows the fastest trapping time observed so far of any intact PSI particle, the PSI core of
C. reinhardtii seems to be best suited to further characterize the electron transfer steps and mechanisms in the reaction center of PSI.
K$K$‐Motives and Koszul duality Eberhardt, Jens Niklas
The Bulletin of the London Mathematical Society,
December 2022, 2022-12-00, Volume:
54, Issue:
6
Journal Article
Peer reviewed
Open access
We construct an ungraded version of Beilinson–Ginzburg–Soergel's Koszul duality for Langlands dual flag varieties, inspired by Beilinson's construction of rational motivic cohomology in terms of ...K$K$‐theory. For this, we introduce and study categories DKS(X)$\hbox{DK}_\mathcal {S}(X)$ of S$\mathcal {S}$‐constructible K$K$‐motivic sheaves on varieties X$X$ with an affine stratification. We show that there is a natural and geometric functor, called Beilinson realisation, from S$\mathcal {S}$‐constructible mixed sheaves DSmix(X)$\hbox{D}^{mix}_\mathcal {S}(X)$ to DKS(X)$\hbox{DK}_\mathcal {S}(X)$. We then show that Koszul duality intertwines the Betti realisation and Beilinson realisation functors and descends to an equivalence of constructible sheaves and constructible K$K$‐motivic sheaves on Langlands dual flag varieties.
The insertion of cobaloxime catalysts in the heme‐binding pocket of heme oxygenase (HO) yields artificial hydrogenases active for H2 evolution in neutral aqueous solutions. These novel biohybrids ...have been purified and characterized by using UV/visible and EPR spectroscopy. These analyses revealed the presence of two distinct binding conformations, thereby providing the cobaloxime with hydrophobic and hydrophilic environments, respectively. Quantum chemical/molecular mechanical docking calculations found open and closed conformations of the binding pocket owing to mobile amino acid residues. HO‐based biohybrids incorporating a {Co(dmgH)2} (dmgH2=dimethylglyoxime) catalytic center displayed up to threefold increased turnover numbers with respect to the cobaloxime alone or to analogous sperm whale myoglobin adducts. This study thus provides a strong basis for further improvement of such biohybrids, using well‐designed modifications of the second and outer coordination spheres, through site‐directed mutagenesis of the host protein.
In the pocket: Novel cobaloxime‐based biohybrids display hydrogenase activity in aqueous media. This study paves the way for inexpensive and effective catalysts for hydrogen production that are capable of functioning in water (see figure). Changes in the coordination environment were investigated by taking advantage of the structural variety of binding pockets of hemoproteins.
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